PROJECT SUMMARY Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder which comprises of a spectrum of hepatic abnormalities ranging from simple steatosis to steatohepatitis (NASH), which can progress to cirrhosis and hepatocellular carcinoma. Despite significant research efforts, the etiology of this disease is poorly understood; in particular, factors associated with progression from steatosis to NASH are unknown. We have developed mouse models from the Hybrid Mouse Diversity Panel (HMDP) that exhibit the spectrum of NAFLD observed in humans. The overall goal of our proposal is to use population-based approaches in mice to identify pathways and higher order biological networks that contribute to the development and progression of NAFLD. Using Mergeomics, an association-based modeling method we developed, we previously identified and validated several genes associated with steatosis from a cohort of HMDP mice fed a high fat, high sucrose diet. Applying the same strategy to a novel transgenic HMDP mice model of NASH, we have now identified several high confidence NASH candidate genes. In Aim 1, we will perform transcriptomic and metabolomics profiling on resistant and susceptible strains to examine the progression of NASH. We will identify and validate candidate genes for NASH progression using multi-omics approaches and Adeno-Associated Virus (AAV) vectors for rapid screening in mice. We will also identify cell-specific changes in gene expression and cell composition related to liver fibrosis and other NAFLD features. This will allow us to follow functional changes in the major hepatic cell types as well as populations of stellate cells and infiltrated inflammatory cells during NASH progression. In Aim 2, we will examine five prioritized genes contributing to hepatic fibrosis, including one gene, Mgp, that we recently validated using knockout mice. Mechanistic studies will be performed to investigate how these genes affect fibrosis. Additional candidate genes identified in Aim 1 will be examined with a similar strategy. Results from these studies will reveal the underlying genetic mechanisms contributing to NAFLD and may identify potential therapeutic targets.